Heart disease is very serious and often requires emergency operations to save lives. A main cause of heart disease is the accumulation of plaque inside the blood vessels, which eventually occludes the blood vessels. Common treatment options available to open up the occluded vessel include balloon angioplasty, rotational atherectomy, and intravascular stents. Traditionally, surgeons have relied on X-ray fluoroscopic images that are planar images showing the external shape of the silhouette of the lumen of blood vessels to guide treatment. Unfortunately, with X-ray fluoroscopic images, there is a great deal of uncertainty about the exact extent and orientation of the stenosis responsible for the occlusion, making it difficult to find the exact location of the stenosis. In addition, though it is known that restenosis can occur at the same place, it is difficult to check the condition inside the vessels after surgery with X-ray.
A currently accepted technique for assessing the severity of a stenosis in a blood vessel, including ischemia causing lesions, is fractional flow reserve (FFR). FFR is a calculation of the ratio of a distal pressure measurement (taken on the distal side of the stenosis) relative to a proximal pressure measurement (taken on the proximal side of the stenosis). FFR provides an index of stenosis severity that allows determination as to whether the blockage limits blood flow within the vessel to an extent that treatment is required. The normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and require treatment.
Often intravascular catheters and guide wires are utilized to measure the pressure within the blood vessel, visualize the inner lumen of the blood vessel, and/or otherwise obtain data related to the blood vessel. To date, guide wires containing pressure sensors, imaging elements, and/or other electronic, optical, or electro-optical components have suffered from reduced performance characteristics compared to standard guide wires that do not contain such components. For example, the handling performance of previous guide wires containing electronic components have been hampered, in some instances, by the limited space available for the core wire after accounting for the space needed for the conductors or communication lines of the electronic component(s), the stiffness of the rigid housing containing the electronic component(s), and/or other limitations associated with providing the functionality of the electronic components in the limited space available within a guide wire.
Further, a problem with existing pressure and flow guide wires is that the coil(s) defining the distal tip of the device can be fragile and prone to unwanted bending or kinking. In that regard, the small diameter and high flexibility of the coil(s) limits the structural integrity that can be provided. Further, the rigid nature of the sensor housing adjacent to the coil(s) causes additional stress to be applied to the coil(s) during use, especially when traversing complex vasculature with many curves and turns. As a result, the handling and performance of the guide wires can be reduced because of the limitations of the coil(s).
Guide wires are designed to be steered through vascular anatomy to suspected lesion sites to allow for treatment of those lesions. There are many desired performance characteristics that have to be considered for the guide wire design: torqueability, support level, tip stiffness, lubricity, smooth transitions, and device compatibility. Regardless of the design needs, good torqueability of the wire tip remains the most important performance output of the wire. Without good torque control of the tip of the wire, physicians have difficulty steering the tip into the appropriate branches to reach the desired lesion.
In order to make a guide wire that meets the desired output requirement, a flexible section of the guide wire (typically the distal most 20 to 40 cm of the wire that will be inserted into the vasculature) can be created via grinding of the core wire to create the desired support and transition conditions. To improve compatibility with other devices that will be advanced over the guide wire, a covering is often placed over the ground section of the core wire and coated with a lubricious coating to improve lubricity. Flexible coverings can include one or more coils, tubes, and/or tubes with integrated spiral coil support. The flexible coverings can be aligned to adjacent components of the guide wire and locked into place at each end via adhesive or solder. These types of flexible coverings are typically attached to the core wire in only two places, at the proximal and distal ends of the flexible covering. In that regard, a rigid adhesive is often used to fixedly secure the ends of the flexible covering to the core wire. The lubricious coatings that are applied to these coverings provide excellent movement in an axial direction within the vasculature and also help devices move smoothly over the wire. However, the traditional use of flexible coverings has a significant deficiency relating to torqueing the tip of the guide wire when the distal section of the guide wire, including the flexible covering, is in tortuosity. In that regard, the more tortuosity that the flexible covering is pushed into and/or the more acute the tortuosity becomes, the more the torqueability of the guide wire tip is degraded.
This degradation in torqueability of the distal section of the guide wire relative to the proximal section of the guide wire occurs because the flexible coverings have very poor torqueability characteristics. For example, when the distal section of the guide wire is in significant tortuosity, as the proximal end of the wire is rotated, the torque is poorly transmitted to the from the core wire to the flexible covering because the flexible covering is typically only attached at each end. This results in the guide wire building up torque with the tip rotation lagging behind the proximal rotation. When the flexible covering is only locked at its ends, the core wire is rotating against a non-lubricious inner surface of the flexible covering and, therefore, not getting the benefit of the lubricity of the outer coating of the flexible covering. At some point, the torque builds up enough to overcome the tortuosity effect on the flexible covering and the flexible covering suddenly spins causing the distal tip of the guide wire to whip through a large angle quickly. This whipping of the distal tip worsens with severe tortuosity and/or increased length of tortuosity. The unwanted whipping of the distal tip can cause problems with placing the guide wire in the desired location within the patient's anatomy and, in severe cases, can even cause damage to the patient's anatomy.
Accordingly, there remains a need for intravascular devices, systems, and methods that include one or more electronic, optical, or electro-optical components and have improved handling characteristics.